Prediction and observation of ring and chain isomers in Sn− i ons

Experimental and theoretical studies have been performed on singly charged anions of sulphur clusters Sn− up to n=9. Density functional calculations with simulated annealing predict the existence of two general classes of structure comprising rings and chains, respectively, with markedly different vertical detachment energies (VDE) for transitions to states of the neutral clusters. VDE and vibration frequencies obtained from photoelectron detachment measurements using a pulsed arc cluster ion source (PACIS) agree well with the calculated values and provide unambiguous spectroscopic evidence for the existence of two types of isomers in both S6− and S7−.